Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.94   10.658%   $96.2061   $96.21   $96.20   $96.20  
  Purchase #2 $141.50   3.650%   $146.6648   $146.66   $146.65   $146.70  
  Purchase #3 $201.55   5.258%   $212.1475   $212.15   $212.15   $212.10  
  Purchase #4 $243.54   12.280%   $273.4467   $273.45   $273.45   $273.40  
  Purchase #5 $153.44   7.639%   $165.1613   $165.16   $165.15   $165.20  
  Purchase #6 $133.52   9.307%   $145.9467   $145.95   $145.95   $145.90  
  Purchase #7 $218.26   7.589%   $234.8238   $234.82   $234.80   $234.80  
  7 purchase totals = $1,178.75       $1,274.3969   $1,274.40   $1,274.35   $1,274.30